1,2,4-Butanetriol is an industrially useful compound which has been known from old times, and it has been used as a synthetic precursor of 3-hydroxytetrahydrofuran and 3-hydroxypyrrolidine derivatives and the like. There have been reported three conventional processes for preparing this compound by the following processes: 1) a process for reducing dimethyl malate with lithium aluminum hydride (J. Amer. Chem. Soc., 103, 9, 2273-2280 (1981)), 2) a process for reducing dimethyl malate with sodium borohydride in a mixed solvent of THF/H2O (J. Org. Chem., 52, 13, 2896-2901 (1987)) and 3) a process for reducing malic acid with a borane-dimethyl sulfide complex in THF (Tetrahedron Lett., 26, 42, 5195-5198 (1985)).
However, the above-mentioned conventional processes had the following problems. First, in the process 1), lithium aluminum hydride, which is difficult to handle industrially and expensive, has to be used as a reducing agent. When an optically active substance is used as the starting material, it is difficult to obtain a target product having a high optical purity, since racemization proceeds during the reaction (J. Org. Chem., 48, 16, 2767-2769 (1983)). Accordingly, it is necessary to carry out troublesome steps wherein a hydroxyl group is protected and then ester groups are reduced to give an optically active target product through deprotection, or a reduced product is converted into its derivative and then the derivative is recrystallized to raise its optical purity. In the process 2), since THF is used as the solvent, it is feared that THF produces a peroxide and the peroxide explodes when THF is concentrated. Accordingly, this process is difficult to apply to industry. In addition, since drain is contaminated by THF to give wastewater and wastewater treatment is necessary, this process has many problems in practice. In the process 3), since dimethyl sulfide gives out a bad smell and it is expensive, it is industrially difficult to use the borane-dimethyl sulfide complex. Since THF is used as the solvent, the above-mentioned fear and wastewater problems are unavoidable.
For these reasons, an economically inexpensive process for obtaining 1,2,4-butanetriol, which is a useful compound as a synthetic intermediate of medicines, agricultural chemicals and the like, by using an easily available compound as a starting material has been desired.
An object of the present invention is to provide a process wherein 1,2,4-butanetriol can be obtained safely, easily and inexpensively without causing the problems concerning wastewater.